dk.netarkivet.wayback
Class LRUCache

java.lang.Object
  dk.netarkivet.wayback.LRUCache

public class LRUCache
extends java.lang.Object

An LRU cache, based on LinkedHashMap.

This cache has a fixed maximum number of elements (cacheSize). If the cache is full and another entry is added, the LRU (least recently used) entry is dropped.

This class is thread-safe. All methods of this class are synchronized.

Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland
Multi-licensed: EPL / LGPL / GPL / AL / BSD. Modified slightly to fit the use of a wayback file cache.

Constructor Summary

LRUCache()
Constructor, where the arguments for the primary constructor is read from settings.

LRUCache(java.io.File dir, int cacheSize)
Creates a new LRU cache.

Method Summary

void	clear() Clears the cache.
java.io.File	get(java.lang.String key) Retrieves an entry from the cache. The retrieved entry becomes the MRU (most recently used) entry.
java.io.File	getCacheDir()
static LRUCache	getInstance()
void	put(java.lang.String key, java.io.File value) Adds an entry to this cache.
int	usedEntries() Returns the number of used entries in the cache.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LRUCache

public LRUCache(java.io.File dir,
                int cacheSize)
         throws IOFailure

Creates a new LRU cache. Using filename as the key, and the cached file as the value.

Parameters:

dir - The directory where the file is stored.

cacheSize - the maximum number of entries that will be kept in this cache.

Throws:

IOFailure

LRUCache

public LRUCache()

Constructor, where the arguments for the primary constructor is read from settings.

Method Detail

getInstance

public static LRUCache getInstance()

Returns:

instance of our Cache

get

public java.io.File get(java.lang.String key)

Retrieves an entry from the cache.
The retrieved entry becomes the MRU (most recently used) entry.

Parameters:

key - the key whose associated value is to be returned.

Returns:

the value associated to this key, or null if no value with this key exists in the cache.

put

public void put(java.lang.String key,
                java.io.File value)

Adds an entry to this cache. The new entry becomes the MRU (most recently used) entry. If an entry with the specified key already exists in the cache, it is replaced by the new entry. If the cache is full, the LRU (least recently used) entry is removed from the cache.

Parameters:

key - the key with which the specified value is to be associated.

value - a value to be associated with the specified key.

clear

public void clear()

Clears the cache.

usedEntries

public int usedEntries()

Returns the number of used entries in the cache.

Returns:

the number of entries currently in the cache.

getCacheDir

public java.io.File getCacheDir()

Returns:

the cacheDir